1. Field of the Invention
The present invention relates to mobile communications, and more particularly to a communication control system, a communication control method, a mobile station and a base station.
2. Description of the Related Art
In general, in the radio communications, signals are received through a plurality of paths and each path is affected by its own delay and fading variation, so that there is a need to carry out a channel estimation for estimating phase and amplitude variations of received signals due to the delay and the fading variation of each path, at a receiver by using a pilot symbol which is a symbol for which the transmission data modulation phase is known in advance.
FIG. 11 shows a part of a configuration of a receiver 10 for carrying out the conventional channel estimation method. Note that FIG. 11 only shows a portion of the configuration of the receiver 10 which is related to the channel estimation.
As shown in FIG. 11, the receiver 10 has a channel estimation device 11 as a device for carrying out the channel estimation, and this channel estimation device 11 has a correlation unit 12 and a path selection unit 13. The correlation unit 12 is connected to the path selection unit 13, receives an input of the pilot symbol in the received signals, produces a delay profile by using this pilot symbol, and transmits the produced delay profile to the path selection unit 13. On the other hand, the path selection unit 13 removes paths that can be regarded as noises from the elements of the delay profile transmitted from the correlation unit 12, selects valid paths, and outputs the delay profile after the path selection as a channel estimation value indicating the state of radio communication channels.
The path selection processing at this path selection unit 13 uses a method in which a reference power level is set as a threshold, a power level of each path is compared with the threshold, and a path for which the power level exceeds the threshold is selected.
However, the conventional channel estimation method fixes the threshold that becomes a reference in carrying out the path selection as described above, so that it has been impossible to carry out the path selection by using the optimum threshold at each occasion, for various radio communication channel states, various service types, various modulation schemes or various MCS (Modulation and Coding Scheme) levels.